The 24-year-old, capped three times by Norway, will fly to Australia in coming days in a big capture for the Jets.
Markussen arrives on a high as well, having helped Valerenga win the Norwegian Women's Cup over the weekend with a 2-1 win over Sandviken in which she scored the 13th minute opener.
"She is dynamic, likes to threaten defences with her pace, has an eye for goal, a great assist-ability and she is a fierce competitor," Jets coach Ash Wilson said.
"Marie has had success through the national youth and senior set ups in Norway, has played in the top leagues of Germany and Norway and is coming to us with UEFA Champions League experience and cup success with her current team at Valerenga."
Markussen isn't the only overseas acquisition for the league, with Canberra United announcing on Tuesday they had signed Ally Haran and Chelsee Washington from US National Women's Soccer League team Orlando Pride.
Haran, a 25-year-old defender, has signed with Canberra on a permanent deal while 23-year-old midfielder Washington is on loan.
The pair will arrive in Australia at the end of the week before beginning training with the United squad on Monday.